Fix internal module reexports (#9378)

# Description
`cargo +stable check` was complaining about ambiguous wildcard
reexports. Fixed by making the reexport of modules not pub as only the
explicitly named symbols are actually needed in the current state.


# User-Facing Changes
None

crates/nu-command/src/strings/format/mod.rs

@@ -1,4 +1,4 @@
-pub mod command;
+mod command;
 mod filesize;
 
 pub use self::filesize::FileSize;